The present invention relates to a method, apparatus and computer program for recording/reproducing moving image data. More particularly, the present invention relates to a method, apparatus and computer program for use in transferring the moving image data through a communication media, storing the moving image data in a storage media, and reading the moving image data.
As a result of technological advancements and widespread use of information networks and information processing devices, the amount of moving image data being transferred through the information networks has been increasing. Since a moving image carries a huge mount of data compared with a still image, generally the moving image data is compressed by a coding system before being transferred. A typical coding system is, for example, Moving Pictures Expect Group (MPEG) coding system as illustrated in FIG. 8.
A coding system for reproducing a still image, is, for example, a progressive reproduction system. When the still image reproduced by this system is displayed through a browser of the Internet, the image first appears on a display screen as an unclear image having low definition. Thereafter, the definition of the image gradually increases until a clear image of a specific definition appears.
When moving image data on a storage media is received through a communication media such as the Internet and is reproduced, the data can only be reproduced up to the stage in which the data has been downloaded. This is so even if MPEG or other coding systems are used. Thus, when moving image data is received or reproduced through a low capacity communication media, viewing the moving image from the start until the end takes a long time since a huge amount of data must be first received then reproduced. Therefore, receiving moving image data in low capacity communication media can be inconvenient.
For example, if a user receives a moving image data for trial purposes, the user is required to view the content of the moving image data from the start until the end, and then judge its usefulness. In order to do this, the user must receive and store the huge amount of data corresponding to the moving image. This huge amount of data must be stored in the storage media of the user""s apparatus regardless of whether all of the data is useful or not. Accordingly, there is an increase in communication costs and a loss of useable capacity of the storage media in the user""s apparatus.
Further, if the user attempts to conduct a direct reproduction from the storage media with a low performance personal computer, making use of software, the user must reproduce each of the moving data from start until the end and view each moving image data. This process takes an exceptionally long period of time.
A conventional technique for handling moving image data is disclosed, for example, in the Japanese Published Unexamined Patent Application No. Hei 9-98430. The following is a brief description of technique wherein the conventional moving image data of a bitmap format is coded by the MPEG coding system and the result is stored in the storage media. This technique sets as an index information identifying particular packets each including an I-picture according to the MPEG coding system an I-picture is inter-frame coded data independent from preceding and succeeding the frame. Further, the technique selectively reads and reproduces each packet including an I-picture during a special mode reproduction such as high-speed reproduction. The technique intends to reduce the burden placed on a decoder. Although the technique is able to reduce the amount of data to be read out during the special mode reproduction, it is not able to perform the reproduction under normal reproduction speed.
Another conventional technique is disclosed, for example, in Japanese Published Unexamined Patent Application No. Hei 5-227515. This conventional technique makes use of hierarchical coding and monolayer coding in accordance with resolutions of the encoder on the transmitting side and the decoder on the receiving side. This technique is intended to achieve an improvement in the coding rate. However, on the receiving side this technique also needs to receive all of the moving image data in order to view the moving image from the start until the end.
The invention provides that on the transmitting side, moving image data is encoded in accordance with a plurality of resolution levels different from each other, and output to communication media in time series by each coded data of each resolution level. On the receiving side the moving image data is reproduced by selecting coded data of an arbitrary resolution level to decode, and reproducing the selected coded data at the arbitrary resolution level from the start until the end.
The invention is able to reproduce the moving image data within an arbitrary range from the start until the end, with less data compared with the conventional technique, and is able to display the moving image data more clearly in accordance with the increase of received data. Thus, the present invention is able to reproduce the moving image progressively. The invention makes use of not only the inter-resolution compression, but also the inter-frame compression to make the stored data even less.